# What is the law of identity and can it be used in the case below?

I read (second comment to this question, which doesn'r offer no solace ar all)

If there are two people who are exactly the same then either they are the same person (via the law of identity) or they are different people.

This sounds like non-sense to me. How can two co-existing people who are exactly the same be the same person? How can a law of identity prevent this? Doesn't the fact that two persons who have a separate existence (in space or in time or in spacetime) already makes them two non-identical persons? What is this "law of identity"?

• The Law of Identity says: For all X ( X = X ). It is one of three Laws of Thought.
– nwr
Jul 11, 2021 at 22:46
• Correct; if "they" are two spatio-temporal distinct entities, they are two and not one. Jul 12, 2021 at 5:56
• This looks like a garbled version of Leibniz's law of identity of indiscernibles mixed with the "law of identity" in old logic. Identity of indiscernibles states, roughly, that if two things are distinct then there is a property distinguishing them (it can be spatiotemporal location for otherwise identical copies). Contrapositively, if two things have all properties identical then they are identical. If the class of properties considered is too small this can be violated. Jul 13, 2021 at 0:51